The angiopoietin-like protein 3 (ANGPTL3) gene was identified from the EST database based on signal sequences and amphipathic helices, and a full-length ANGPTL3 cDNA was subsequently isolated from a human fetal liver/spleen cDNA library (Conklin et al., 1999, Genomics 62: 477-482). The deduced 460-amino acid hANGPTL3 protein shares 76% amino acid sequence identity with mouse ANGPTL3 and has the characteristic structure of angiopoietins; i.e., a signal peptide, an extended helical domain predicted to form dimeric or trimeric coiled-coils, a short linker peptide, and a globular fibrinogen homology domain (FD) (Conklin et al., 1999, supra). ANGPTL3 contains the 4 conserved cysteine residues implicated in the intramolecular disulfide bonds within the FD; however, ANGPTL3 contains neither the two additional cysteines nor the characteristic calcium-binding motif found in the FDs of angiopoietins (ANGs; i.e., ANG1, ANG2 and ANG4) (Conklin et al., 1999, supra), which are protein growth factors that promote angiogenesis. In addition, unlike ANGs, ANGPTL3 does not bind to Tie2; however, it may also induce angiogenesis by binding to integrin αvβ3 via its C-terminal FD (Camenisch et al., 2002, J Biol Chem 277:17281-17290).
Comprehensive in vivo data were obtained from the outbred KK mouse model, which is moderately obese with abnormally high levels of plasma insulin, glucose, and lipids, resembling type 2 diabetes mellitus in humans (Koishi et al., 2002, Nature Genetics 30:151-157). One sub-strain of mouse, the KK/San, however, was found to exhibit abnormally low plasma lipid levels (hypolipidemia), which were inherited as a Mendelian recessive. The loci was mapped to chromosome 4 and eventually identified to be the gene encoding ANGPTL3, which contained a 4-bp nucleotide sequence insertion in exon 6 (Koishi et al., 2002, supra). Conversely, plasma lipid levels increase after adenovirus-mediated transfer of ANGPTL3 gene, or after administration of recombinant human ANGPTL3 in KK/San mice. This effect was not mediated by changes in genes involved in cholesterol synthesis, lipoprotein clearance or NEFA oxidation (Koishi et al., 2002, supra). Further, in vitro analysis of recombinant protein showed that ANGPTL3 directly inhibits lipoprotein lipase (LPL) activity, indicating that it is a lipid metabolism modulator that regulates very low density lipoprotein (VLDL) triglyceride levels through the inhibition of LPL activity (Shimizugawa et al., 2002, J Biol Chem 277(37):33742-33748). It has been shown that the N-terminal coiled-coil domain, especially the N-terminal region residues 17-165, and not the C-terminal FD, of ANGPTL3, is required for its activity of increasing plasma triglyceride levels in mice (Ono et al., 2003, J Biol Chem 278:41804-41809).
The amino acid and nucleotide sequences of human ANGPTL3 are shown in SEQ ID NOS:161 and 162, respectively. Antibodies to ANGPTL3 are disclosed in, for example, WO2008/073300 and U.S. Pat. No. 7,935,796.